1. Field of the Invention
The present invention relates to a bolt tightening tool for tightening a nut onto a bolt, and more particularly to such a bolt tightening tool which may prevent incomplete fitting of a tip of a bolt in an inner sleeve of the tool.
2. Description of the Prior Art
In general, a bolt tightening tool includes an inner sleeve and an outer sleeve which are coupled to a drive. The inner sleeve is fitted to a tip of a bolt to be sheared, and the outer sleeve is fitted to a nut screwed on the bolt. The outer sleeve is rotated by the drive to thereby tighten the nut onto the bolt. Simultaneously therewith, the tip in the inner sleeve is sheared as it is subjected to the tightening reaction of the outer sleeve applied to the nut.
In such a bolt tightening tool, however, even when the tip has been fitted in the inner sleeve incompletely, the nut will be fitted in the outer sleeve, causing the latter to rotate. This causes damage to the tip or the bolt and allows the tightening reaction to act inadvertently on the operator by way of the tightening tool, thereby resulting in accident.
Various devices and systems have been devised heretofore to eliminate the aforenoted disadvantages. For example, U.S. Pat. Nos. 4,403,529 and 4,503,736 disclose means for preventing incomplete fitting of a tip of a bolt wherein an inner sleeve is allowed to retract only when the tip is fitted in the inner sleeve completely or properly, thereby permitting an outer sleeve to receive a nut therein. The mechanisms disclosed in these patents, however, are complicated in construction, and the number of components is increased including, for example, means for sensing complete fitting of a tip into a tip receiving bore and means for temporarily holding a sheared tip. Thus, the assembling procedure is cumbersome, and the mechanisms or devices are relatively expensive to manufacture.